Ta có:
\(A=\frac{1}{3}-\frac{1}{3^2}+\frac{1}{3^3}-\frac{1}{3^4}+...+\frac{1}{3^{99}}-\frac{1}{3^{100}}\)
=> \(3A=1-\frac{1}{3}+\frac{1}{3^2}-\frac{1}{3^3}+...+\frac{1}{3^{98}}-\frac{1}{3^{99}}\)
=> \(A+3A=1-\frac{1}{3^{100}}\)
=> \(4A=\frac{3^{100}-1}{3^{100}}\)
=> \(A=\frac{3^{100}-1}{4.3^{100}}\)
Tính
A=1*2+2*3+3*4+..+99*100
B=1*3+3*5+5*7+..+97*99
C=1*2*3+2*3*4+...+98*99*100
tính
a=1*2+2*3+3*4+....+99*100
b=1*3+3*5+5*7+....97*99
c=1*2*3+2*3*4+...98*99*100
giải dùm mk nhoa
Tính
A=1+3^1-3^2+3^3-3^4+...........+3^99-3^100
B=50.(51^99+51^98+51^97+......+51^1+1)+1
Bài 4: Tính tổng 1) 1 + (-2) + 3 + (-4) + . . . + 19 + (-20) 2) 1 – 2 + 3 – 4 + . . . + 99 – 100 3) 2 – 4 + 6 – 8 + . . . + 48 – 50 4) – 1 + 3 – 5 + 7 - . . . . + 97 – 99 5) 1 + 2 – 3 – 4 + ... + 97 + 98 – 99 - 100
Tính nhanh
A=1/3-1/3^2+1/3^3-1/3^4+.......+1/3^99-1/3^100
Tính tổng 100-(1+1/2+1/3+1/4+...+1/100)/1/2+2/3+3/4+....+99/100
Tính nhanh
a) 1 + 2 + 3 + … + 99 + 100 b) 2 + 4 + 6 + … + 96 + 98
c) (–1) + 2 + (–3) + 4 + … + (–99) +100 d) –1 + 2 – 3 + 4 – … – 99 + 100
Tính :
A = 1 . 2 + 2 . 3 + 3 . 4 + ... + 99 . 100
B = 1 . 3 + 2 . 4 + 3 . 5 + ... + 99 . 100
C = 1 . 4 + 2 . 5 + 3 . 6 + ... + 99 . 102
D = 4 + 12 + 24 + ... + 19404 + 19800
E = 1 + 3 + 6 + 10 + ... + 4851 + 4950
Chứng minh rằng :
a,1- 1/2 + 1/3 - 1/4 + 1/5 - 1/6 + ...... + 1/ 99 - 1/ 100 = 1 / 51 + 1/ 52 + 1/ 53 + ... + 1/ 100
b, A= 1/3 - 2/ 32 + 3/ 33 - 4/ 34 + .... + 99/ 399 - 100/ 3100 < 3/ 16
Help me!!!Thanks các pạn nhìu nha.
Tính hợp lý:
1)(1/2+1/3+1/4+...+1/100):(99/1+98/2+97/3+...+1/99)
2)A=1/3+1/3^2+1/3^3+...+1/3^99
3)4^5.9^4-2.6^9/2^10.3^8+6^8.20
